Serine proteases are a subgroup of carbonyl hydrolase. They comprise a diverse class of enzymes having a wide range of specificities and biological functions. Stroud, R. Sci. Amer., 131:74–88. Despite their functional diversity, the catalytic machinery of serine proteases has been approached by at least two genetically distinct families of enzymes: the subtilisins and the mammalian chymotrypsin related and homologous bacterial serine proteases (e.g., trypsin and S. gresius trypsin). These two families of serine proteases show remarkably similar mechanisms of catalysis. Kraut, J. (1977), Ann. Rev. Biochem., 46:331–358. Furthermore, although the primary structure is unrelated, the tertiary structure of these two enzyme families bring together a conserved catalytic triad of amino acids consisting of serine, histidine and aspartate.
Subtilisin is a serine endoprotease (MW 27,500) which is secreted in large amounts from a wide variety of Bacillus species and other microorganisms. The protein sequence of subtilisin has been determined from at least four different species of Bacillus. Markland, F. S., et al. (1983), Hoppe-Seyler's Z. Physiol. Chem., 364:1537–1540. The three-dimensional crystallographic structure of Bacillus amyloliquefaciens subtilisin to 2.5 Å resolution has also been reported. Wright, C. S., et al. (1969), Nature, 221:235–242; Drenth, J., et al. (1972), Eur. J. Biochem., 26:177–181. These studies indicate that although subtilisin is genetically unrelated to the mammalian serine proteases, it has a similar active site structure. The x-ray crystal structures of subtilisin containing covalently bound peptide inhibitors (Robertus, J. D., et al. (1972), Biochemistry, 11:2439–2449) or product complexes (Robertus, J. D., et al. (1976), J. Biol. Chem., 251:1097–1103) have also provided information regarding the active site and putative substrate binding cleft of subtilisin. In addition, a large number of kinetic and chemical modification studies have been reported for subtilisin (Philipp, M., et al. (1983), Mol. Cell. Biochem., 51:5–32; Svendsen, B. (1976), Carlsberg Res. Comm., 41:237–291; Markland, F. S. Id.) as well as at least one report wherein the side chain of methionine at residue 222 of subtilisin was converted by hydrogen peroxide to methionine-sulfoxide (Stauffer, D. C., et al. (1965), J. Biol. Chem., 244:5333–5338) and the side chain of serine at residue 221 converted to cysteine by chemical modification (Polgar, et al. (1981), Biochimica et Biophysica Acta, 667:351–354.)
U.S. Pat. No. 4,760,025 (RE 34,606) discloses the modification of subtilisin amino acid residues corresponding to positions in Bacillus amyloliquefaciens subtilisin tyrosine −1, aspartate +32, asparagine +155, tyrosine +104, methionine +222, glycine +166, histidine +64, glycine +169, phenylalanine +189, serine +33, serine +221, tyrosine +217, glutamate +156 and alanine +152. U.S. Pat. No. 5,182,204 discloses the modification of the amino acid +224 residue in Bacillus amyloliquefaciens subtilisin and equivalent positions in other subtilisins which may be modified by way of substitution, insertion or deletion and which may be combined with modifications to the residues identified in U.S. Pat. No. 4,760,025 (RE 34,606) to form useful subtilisin mutants or variants. U.S. Pat. No. 5,155,033 discloses similar mutant subtilisins having a modification at an equivalent position to +225 of B. amyloliquefaciens subtilisin. U.S. Pat. Nos. 5,185,258 and 5,204,015 disclose mutant subtilisins having a modification at positions +123 and/or +274. The disclosure of these patents is incorporated herein by reference, as is the disclosure of U.S. patent application Ser. No. 07/898,382, which discloses the modification of many amino acid residues within subtilisin, including specifically +99, +101, +103, +107, +126, +128, +135, +197 and +204. All of these patent /applications are commonly owned. U.S. Pat. No. 4,914,031 discloses certain subtilisin analogs, including a subtilisin modified at position +76. The disclosure of this patent is also incorporated herein by reference. The particular residues identified herein and/or the specific combinations claimed herein, however, are not identified in these references.
Accordingly, it is an object herein to provide carbonyl hydrolase (preferably subtilisin) variants containing the substitution of a plurality of amino acid residues in the DNA encoding a precursor carbonyl hydrolase corresponding to positions +76 in combination with one or more positions selected from the group +99, +101, +103, +104, +107, +123, +27, +105, +109, +126, +128, +135, +156, +166, +195, +197, +204, +206, +210, +216, +217, +218, +222, +260, +265 and/or +274 in Bacillus amyloliquefaciens subtilisin. Such variants generally have at least one property which is different from the same property of the carbonyl hydrolase precursor from which the amino acid sequence of said variant is derived.
It is a further object to provide DNA sequences encoding such carbonyl hydrolase variants, as well as expression vectors containing such variant DNA sequences.
Still further, another object of the invention is to provide host cells transformed with such vectors, as well as host cells which are capable of expressing such DNA to produce carbonyl hydrolase variants either intracellularly or extracellularly.
The references discussed above are provided solely for their disclosure prior to the filing date of the instant case, and nothing herein is to be construed as an admission that the inventors are not entitled to antedate such disclosure by virtue of a prior invention or priority based on earlier filed applications.